MongoDB query traverse through array of object and choose specific object

Question

MongoDB query to get last/all objects from array

{
    WholeData:[
        {
            EnteredAmount:100,
            OverPayment:0,
            Type:"payment",
        },
        {
            EnteredAmount:200,
            OverPayment:0,
            Type:"payment",
        },
    ]
}

{
    WholeData:[
        {
            EnteredAmount:600,
            OverPayment:0,
            Type:"refund",
        },
        {
            EnteredAmount:400,
            OverPayment:0,
            Type:"refund",
        },
    ]
}

This is how sample documents looks like
I want to write a query which results something like if type is refund then push/keep all array objects else push/keep only the last index object. sample output should be

{
    WholeData:[

        {
            EnteredAmount:200,
            OverPayment:0,
            Type:"payment",
        },
    ]
}



{
    WholeData:[
        {
            EnteredAmount:600,
            OverPayment:0,
            Type:"refund",
        },
        {
            EnteredAmount:400,
            OverPayment:0,
            Type:"refund",
        },
    ]
}

its a long query already. that alright if it can be done in multiple pipelines — Faizan Ahmed
– Faizan Ahmed, Commented Sep 9, 2021 at 12:29

mohammad Naimi · Accepted Answer · 2021-09-10 06:26:19Z

1

first we create a another array to store last element of WholeData if Type:"payment" then create project and check if WholeData was empty means type is refund else payment and create our result use this aggregation

db.collection.aggregate([
[
   {
    '$addFields': {
      'WholeDataP': {
        '$filter': {
          'input': '$WholeData', 
          'as': 'z', 
          'cond': {
            '$and': [
              {
                '$eq': [
                  {
                    '$indexOfArray': [
                      '$WholeData', '$$z'
                    ]
                  }, {
                    '$sum': [
                      {
                        '$size': '$WholeData'
                      }, -1
                    ]
                  }
                ]
              }, {
                '$ne': [
                  '$$z.Type', 'refund'
                ]
              }
            ]
          }
        }
      }
    }
  }, {
    '$project': {
      'WholeData': {
        '$cond': [
          {
            '$eq': [
              {
                '$size': '$WholeDataP'
              }, 0
            ]
          }, '$WholeData', '$WholeDataP'
        ]
      }
    }
  }
]
])

edited Sep 10, 2021 at 6:26

answered Sep 9, 2021 at 15:04

mohammad Naimi

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2 Comments

Faizan Ahmed Over a year ago

you understand it a bit different if type is refund then all array element other wise last element and type can be payment, invoice or some other strings only for refund i need all elements and for all other i need last element

Faizan Ahmed Over a year ago

yes i did exactly the same. changed $eq to $ne and refund and your change is also same. If you can explain little the and portion of the query whats exactly happening in that whole aggregation. Thanks.

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